Fix detector center coordinates

Use view-local coordinates for the detector center because
its drawing, touch handling, and crop ROI math all operate
in the view's own coordinate space.

This avoids offset crop overlays when the view is not laid
out at the parent's origin.

app/src/main/kotlin/de/markusfisch/android/binaryeye/widget/DetectorView.kt

@@ -247,8 +247,8 @@ class DetectorView : View {
 		viewWidth = right - left
 		viewHeight = bottom - top
 		center.set(
-			left + (viewWidth / 2),
-			top + (viewHeight / 2)
+			viewWidth / 2,
+			viewHeight / 2
 		)
 		minY = padding * 2
 		maxY = viewHeight - minY